Demand for color head- and helmet-mounted displays (HMDs) is growing. Interest focuses on full-color systems, but a limited color repertoire is sufficient for some applications and can reduce cost and complexity significantly, especially when implemented using subtractive-color active-matrix liquid-crystal display (AMLCD) technology. Recently, Honeywell completed an extensive series of human factors experiments to answer important questions about the design and merits of two-primary subtractive-color AMLCDs for HMD applications. Our main conclusion is that a subtractive-color AMLCD with high aperture ratio should yield better image quality than a comparable spatially integrative AMLCD. Making use of a two-primary display's ability to produce mixture colors (e.g., yellow and orange) could also prove beneficial. This paper summarizes the experiments and findings that lead to these and other conclusions.